title: Investigation on mechanism of Cr(VI) reduction and removal by Bacillus amyloliquefaciens, a novel chromate tolerant bacterium isolated from chromite mine soil.
abstract: A strain CSB 9 isolated from chromite mine soil of Sukinda, India was identified as Bacillus amyloliquefaciens based on biochemical and 16S rRNA gene sequencing. The strain exhibited relatively high tolerance to Cr(VI) (⩽900mgL(-1)) and fast reduction rate of 2.22mg Cr(VI) L(-1)h(-1), under optimized conditions of 100mgL(-1) Cr(VI), pH 7 and temperature 35°C within 45h. Mechanism of Cr(VI) reduction as well as nature and fate of the reduced product were studied to determine the scope of removal of reduced Cr(III) end product. AAS analyses of the culture products treated with Cr(VI) for 45h showed the distribution of Cr(III) in pellet and culture supernatant to be 37.4±1.7 and 62.6±3.4mgL(-1), respectively. In SEM images, the bacterial pellets with Cr(VI) treatment appeared coagulated, rough and porous whereas the pellets without Cr(VI) treatment appeared regular, smooth and non-porous in structure. SEM-EDX of the bacterial precipitates under Cr(VI) treatment revealed immobilization of Cr(III) species on the bacterial cell surface. Further Raman spectroscopy analysis confirmed the presence of Cr(III) species, with characteristic peak at around 600cm(-1). TEM-EDX study of the bacterial precipitates under Cr(VI) treatment showed intracellular deposition of Cr(III) which are in nanometric range. Further characterization of reduced product by XRD, FT-IR and SAED analyses suggested the formation of poorly crystalline end products. A Cr(VI) removal mechanism considering both the surface immobilization and intracellular accumulation of Cr(III) along with the formation of coagulated cell precipitate by living B. amyloliquefaciens was suggested.
authors.affiliation: Department of Biotechnology, College of Engineering and Technology, Biju Patnaik University of Technology, Techno-Campus, Ghatikia, Bhubaneswar 751003, Odisha, India.
authors.forename: Sasmita
authors.initials: S
authors.lastname: Das
authors.forename: Jigni
authors.initials: J
authors.lastname: Mishra
authors.forename: Saroj Kumar
authors.initials: SK
authors.lastname: Das
authors.forename: Sony
authors.initials: S
authors.lastname: Pandey
authors.forename: Danda Srinivas
authors.initials: DS
authors.lastname: Rao
authors.forename: Anindita
authors.initials: A
authors.lastname: Chakraborty
authors.forename: Mathummal
authors.initials: M
authors.lastname: Sudarshan
authors.forename: Nigamananda
authors.initials: N
authors.lastname: Das
authors.forename: Hrudayanath
authors.initials: H
authors.lastname: Thatoi
mesh_terms: D001407:Bacillus / Q000145:classification / Q000378:metabolism* / Q000502:physiology; D001673:Biodegradation, Environmental; D002857:Chromium / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007194:India; D008906:Mining; D012987:Soil; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000032:analysis / Q000378:metabolism*; D013696:Temperature
chemical_list: D012987:Soil; D012989:Soil Pollutants; D002857:Chromium; C074702:chromium hexavalent ion
keywords: Bacillus amyloliquefaciens; Bioremediation; Cr(VI) reduction; Hexavalent chromium; Reduced product characterization